For an introduction of pneumatic vibration isolation systems, reference may be had to a paper by Professor Daniel B. DeBra, entitled "Design of Laminar Flow Restrictors for Damping Pneumatic Vibration Isolators" (CIPR 34th General Assembly, August 1984).
In particular, FIG. 5 of that article and its accompanying text illustrate and describe the typical pneumatic vibration isolator. As shown in U.S. Pat. No. 3,627,246, by Fred B. Widding, issued Dec. 14, 1971 for "Isolating Leg Structure for Tables and the Like," such pneumatic vibration isolators use a rolling diaphragm which extends over or at least between the piston and a circular edge of the compliance or spring chamber.
In that classical approach to pneumatic vibration isolation, almost the entire pressure load is supported by the piston head, and only a small amount of the pneumatic pressure is supported by the necessarily narrow convolution of the circumferential rolling or compliance section of the diaphragm. Horizontal pressure components acting on a cylindrical side of: the piston on the one hand and on an adjacent wall of an annular diaphragm mount or clamp on the other hand act in opposition and thereby cancel each other out. The vertical pressure components appear as a normal pressure on the projection of the small semicircularly shaped segment of the rolling diaphragm convolution. Even the sum of such vertical pressure components around the piston is small, such as on the order of two percent of the total pressure on the piston head or on the part of the diaphragm carried by or carrying the piston head.
The function of such rolling diaphragm in prior-art vibration isolators thus was and is to separate the piston from the top or bottom section of the adjacent pneumatic chamber, as the case may be.
Also, the classical vibration isolator typified in the above mentioned FIG. 5 of Professor DeBra's article, was and is oriented in terms of vertical vibration isolation, with some horizontal vibration isolation being provided by the flexible rubber sheeting of prior-art diaphragms.
However, as pointed out in U.S. Pat. No. 3,784,146, by Dr. John W. Matthews, issued Jan. 8, 1974 for "Horizontal Vibration Isolation System," col. 1, lines 26 to 30:
"Attempts to make such a diaphragm system more effective with horizontal vibrations have either resulted in reduced performance in the vertical direction or in poor stability in the horizontal direction."
Accordingly, that pivotal Matthews patent provided the piston with an internal cable suspension system that has been leading technology for pneumatic vibration isolation systems for isolating loads from vertical and horizontal vibrations.
Other approaches to the problem are apparent from U.S. Pat. No. 4,360,184, by Willis J. Reid, III, issued Nov. 23, 1982 for "Pneumatic Device for Attenuation of Vertical, Horizontal and Rotational Dynamic Forces." That approach retained the classical piston-and-diaphragm configuration wherein the diaphragm supports only a small portion of the pneumatic pressure essentially only in the necessarily narrow convolution of the circumferential rolling section of the diaphragm, as explained above. Almost the entire pressure load is again supported by the piston head at least partially covered by the diaphragm, and by the head of a piston well for presenting a bearing surface to a load support rod. Such an extension of the load support pivot beyond the vertical roll center (VRC) of the diaphragm was designed to increase the range of vertical and horizontal vibration down to the 5 Hz area. A second embodiment provides a secondary piston with secondary diaphragm where the first embodiment provides the bearing surface.
Such prior-art approaches logically make for bulky, heavy and expensive structures. Also, their efficacy in isolating loads from rotational vibratory components is questionable.